diff --git a/frontend/src/js/misc/wb-disable-controls.js b/frontend/src/js/misc/wb-disable-controls.js
new file mode 100644
index 0000000..251d260
--- /dev/null
+++ b/frontend/src/js/misc/wb-disable-controls.js
@@ -0,0 +1,12 @@
+function wbDisableControls() {
+  $('input, select, button').attr('disabled', 'disabled');
+  $('a').each(function() { $(this).data('old_href', $(this).attr('href')); });
+  $('a').attr('href', null);
+}
+
+function wbEnableControls() {
+  $('input, select, button').attr('disabled', null);
+  $('a').each(function() { $(this).attr('href', $(this).data('old_href')); });
+}
+
+export { wbEnableControls, wbDisableControls };
diff --git a/frontend/src/js/page/wb-launch-workflow-page.js b/frontend/src/js/page/wb-launch-workflow-page.js
index 6b0cdfe..322ccf2 100644
--- a/frontend/src/js/page/wb-launch-workflow-page.js
+++ b/frontend/src/js/page/wb-launch-workflow-page.js
@@ -1,10 +1,12 @@
 import { h, Component, createRef } from 'preact';
+import { route } from 'preact-router';
 import WBNavbarCommon from 'wb-navbar-common';
 import WBArvadosCrumbs from 'wb-arvados-crumbs';
 import WBBrowseDialog from 'wb-browse-dialog';
 import WBTable from 'wb-table';
 import WBNameAndUuid from 'wb-name-and-uuid';
 import makeArvadosRequest from 'make-arvados-request';
+import { wbDisableControls, wbEnableControls } from 'wb-disable-controls';
 import linkState from 'linkstate';
 
 function parseDefinition(text) {
@@ -21,6 +23,41 @@ function encodeURIComponentIncludingDots(s) {
   return encodeURIComponent(s).replace('.', '%2E');
 }
 
+function inputSpecInfo(inputSpec) {
+  const isFile = (inputSpec.type === 'File' || inputSpec.type === 'File[]' ||
+    (inputSpec.type.type === 'array' && inputSpec.type.items === 'File'));
+
+  const isDirectory = (inputSpec.type === 'Directory' || inputSpec.type === 'Directory[]' ||
+    (inputSpec.type.type === 'array' && inputSpec.type.items === 'Directory'));
+
+  const isArray = (inputSpec.type === 'File[]' || inputSpec.type === 'Directory[]' ||
+    inputSpec.type.type === 'array');
+
+  return { isFile, isDirectory, isArray };
+}
+
+function uuidsToCwl(obj, isFile) {
+  if (obj instanceof Array) {
+    const res = {};
+    for (let k in obj) {
+        res[k] = uuidsToCwl(obj[k], isFile);
+    }
+    return res;
+  }
+
+  if (typeof(obj) === 'string' &&
+    (/^[0-9a-z]{5}-[0-9a-z]{5}-[0-9a-z]{15}/.exec(obj) ||
+      /^[0-9a-f]{32}\+[0-9]+/.exec(obj))) {
+
+    return {
+      'class': (isFile ? 'File' : 'Directory'),
+      'location': 'keep:' + obj
+    };
+  }
+
+  throw Error('Expected Arvados path or array of paths');
+}
+
 class WBPathDisplay extends Component {
   fetchData() {
     const { app, path } = this.props;
@@ -67,6 +104,7 @@ class WBLaunchWorkflowPage extends Component {
     super(...args);
     this.browseDialogRef = createRef();
     this.state.inputs = {};
+    this.state.errors = [];
   }
 
   componentDidMount() {
@@ -86,14 +124,7 @@ class WBLaunchWorkflowPage extends Component {
   renderInput(inputSpec) {
     const { app } = this.props;
 
-    const isFile = (inputSpec.type === 'File' || inputSpec.type === 'File[]' ||
-      (inputSpec.type.type === 'array' && inputSpec.type.items === 'File'));
-
-    const isDirectory = (inputSpec.type === 'Directory' || inputSpec.type === 'Directory[]' ||
-      (inputSpec.type.type === 'array' && inputSpec.type.items === 'Directory'));
-
-    const isArray = true; // (inputSpec.type === 'File[]' || inputSpec.type === 'Directory[]' ||
-      // inputSpec.type.type === 'array');
+    const { isFile, isDirectory, isArray } = inputSpecInfo(inputSpec);
 
     if (!isFile && !isDirectory)
       return (
@@ -153,9 +184,97 @@ class WBLaunchWorkflowPage extends Component {
     );
   }
 
+  submit() {
+    // first see if all inputs are parseable
+    const inputs = {};
+    const errors = [];
+
+    const { workflowDefinition } = this.state;
+    const main = workflowDefinition['$graph'].find(a => (a.id === '#main'));
+
+    for (let k in this.state.inputs) {
+      try {
+        let val = jsyaml.safeLoad(this.state.inputs[k]);
+        const { isFile } = inputSpecInfo(main.inputs.find(a => (a.id === k)));
+        val = uuidsToCwl(val, isFile);
+        k = k.split('/').slice(1).join('/');
+        inputs[k] = val;
+      } catch (exc) {
+        errors.push('Error parsing ' + k + ': ' + exc.message);
+      }
+    }
+
+    if (errors.length > 0) {
+      this.setState({ errors });
+      return;
+    }
+
+    // prepare a request
+    const { app, workflowUuid } = this.props;
+    const { processName, processDescription,
+      defaultProcessName, defaultProcessDescription,
+      projectUuid } = this.state;
+    const { arvHost, arvToken, currentUser } = app.state;
+    const req = {
+      name: processName || defaultProcessName,
+      description: processDescription || defaultProcessDescription,
+      owner_uuid: projectUuid || currentUser.uuid,
+      container_image: 'arvados/jobs',
+      properties: {
+        template_uuid: workflowUuid
+      },
+      runtime_constraints: {
+        API: true,
+        vcpus: 1,
+        ram: 1073741824
+      },
+      cwd: '/var/spool/cwl',
+      command: [
+        'arvados-cwl-runner',
+        '--local',
+        '--api=containers',
+        '--project-uuid=' + (projectUuid || currentUser.uuid),
+        '--collection-cache-size=256',
+        '/var/lib/cwl/workflow.json#main',
+        '/var/lib/cwl/cwl.input.json'],
+      output_path: '/var/spool/cwl',
+      priority: 1,
+      state: 'Committed',
+      mounts: {
+        'stdout': {
+          kind: 'file',
+          path: '/var/spool/cwl/cwl.output.json'
+        },
+        '/var/spool/cwl': {
+          kind: 'collection',
+          writable: true
+        },
+        '/var/lib/cwl/workflow.json': {
+          kind: 'json',
+          content: workflowDefinition
+        },
+        '/var/lib/cwl/cwl.input.json': {
+          kind: 'json',
+          content: inputs
+        }
+      }
+    };
+
+    wbDisableControls();
+    let prom = makeArvadosRequest(arvHost, arvToken,
+      '/arvados/v1/container_requests',
+      { method: 'POST', data: JSON.stringify(req) });
+    prom = prom.then(xhr => {
+      wbEnableControls();
+      route('/process/' + xhr.response.uuid);
+    });
+
+    // throw Error('Not implemented');
+  }
+
   render({ app, workflowUuid },
     { workflow, workflowDefinition, projectUuid, processName, processDescription,
-    defaultProcessName, defaultProcessDescription }) {
+    defaultProcessName, defaultProcessDescription, errors }) {
 
     return (
       <div>
@@ -221,6 +340,16 @@ class WBLaunchWorkflowPage extends Component {
                 Submit
               </button>
             </div>
+
+            { errors.length > 0 ? (
+              <div class="form-group">
+                { errors.map(err => (
+                  <div class="alert alert-danger" role="alert">
+                    { err }
+                  </div>
+                ))}
+              </div>
+            ) : null }
           </form>) : <div>Loading...</div> }
       </div>
     );